A step in downlink received signal processing in long term evolution (LTE) network is to synchronize the carrier frequencies between the transmitter and the receiver, e.g., between the base station (BS) or evolved nodcB (eNB) and the user equipment (UE) or mobile station (MS). This synchronization is performed to enable the UE/MS to decode the signal from the eNB/BS. Herein the terms eNB will also be used to refer to a BS, an access point, etc. The term UE will also be used to refer to a MS, mobile device, cellular phone, etc. Carrier frequency offset (CFO) estimation and compensation scheme may be performed by the UE based on standardized reference symbols.
Currently, the reference signals often used for this purpose are cell-specific reference signals (CRS) that are defined in the LTE standard. However, with the introduction of coordinated multipoint processing (CoMP) techniques, CRS signals have become less applicable for CFO estimation because there may be some cases when several neighboring eNBs transmit the same CRS waveform, e.g., in CoMP scenario 4, where low-power remote radio heads (RRHs) within the coverage of the high-power macro cell may operate with the same cell ID, e.g. as the Macro cell. When several neighboring eNBs transmit the same CRS waveform, CFO estimation for each eNB becomes difficult, i.e., multiple eNBs may use carrier frequencies that are too close to one another. The UE cannot determine which eNB sent which CRS waveform when two CRS waveforms are the same. Another drawback of using CRS signals for CFO estimation is the lack of the ability to manage interference on the CRS signals for CoMP techniques. This results in poor quality of the received CRS signals. Interference causes errors in the estimation processes. This prevents the UE from tuning to the proper frequency.